JP4637650B2 - Exposure apparatus and gradation correction method in exposure apparatus - Google Patents

Description

  The present invention relates to an exposure apparatus including an exposure head in which light emitting elements made of organic EL are arranged, and a gradation correction method in the exposure apparatus.

  2. Description of the Related Art Conventionally, an apparatus that exposes a photosensitive material to form an image using an exposure head composed of a line-shaped light emitting element array in which a plurality of light emitting elements are arranged in a line is known. This type of exposure head is usually configured such that a lens array is combined with a line-shaped light emitting element array, and the photosensitive material to be exposed is irradiated with light condensed by the lens array. This lens array is formed by assembling a plurality of equal-magnification imaging lenses, each of which collects light emitted from the light-emitting elements of the line-shaped light-emitting element array, in a state of being arranged substantially parallel to the light-emitting element arrangement direction. .

  An exposure apparatus using such an exposure head holds a photosensitive material at a position where light emitted from the exposure head is irradiated, and the photosensitive material and the exposure head are arranged in the direction in which the light emitting elements are arranged in the line-shaped light emitting element array. Sub-scanning means for relatively moving in the sub-scanning direction substantially orthogonal to the (main scanning direction) is further provided.

  When the amount of light emitted from the light emitting element array on the photosensitive material is different for each light emitting element, the exposure apparatus exposes an image having portions having the same density or hue in the main scanning direction. At this time, a density step or a hue step occurs in that portion. And such a level | step difference will extend long in the direction of this subscanning with subscanning, and will appear as what is called a stripe | line | muscle nonuniformity.

  Therefore, in general, all elements emit light under the same driving conditions, the amount of light emitted is measured for each element, the correction coefficient of each element is determined so that the amount of light emitted from all elements is uniform, and the actual operating state In FIG. 5, the exposure amount is made uniform by driving each element under a driving condition (driving voltage, driving current, light emission time) corresponding to the correction coefficient (for example, see Patent Document 1). For example, as a result of the light amount deviation correction, an element with a low light emission amount is used with an increased driving current or lighting time, and an element with a high light emission amount is used with a reduced driving current or lighting time.

  Further, in response to increasing demands for high image quality of an exposure image, Patent Document 2 proposes a method of correcting gradation characteristics for each pixel (each light emitting element) in an exposure apparatus using a light emitting element array. Here, there is disclosed a method for rechecking the gradation characteristics and correcting the error when the light amount of the exposure light source changes by a threshold value or more. First, when the light amount measurement is performed with two gradations and the light amount fluctuation is the threshold value or more, Further, there is exemplified a method for performing gradation correction by performing re-photometry for four gradations.

  As an exposure light source (light emitting element) for recording an image on a photosensitive material, LED, PLZT, liquid crystal, VFTH, and the like are employed. In recent years, exposure using an organic EL element (electroluminescence) element is employed. Various heads have been proposed, and an exposure apparatus that exposes a two-dimensional image on the photosensitive material by performing sub-scanning by relatively moving the exposure head composed of such an organic EL light emitting element array and the photosensitive material is also known. (For example, see Patent Document 3).

  Since the organic EL element has a large decrease in luminance due to the cumulative lighting time compared to other light emitting elements, the exposure amount decreases and the print density changes when the apparatus is operated for a long period of time. Therefore, when an organic EL element is used as an exposure light source, periodic light amount correction is essential, and a light amount correction unit such as that described in Patent Document 1 is mounted in the apparatus, and the light amount is periodically emitted. There is a need to make corrections.

Conventionally, it has been known that an organic EL element has a phenomenon called edge growth in which a light emitting area (light emitting region) is reduced with time, and it is a problem that the amount of light emission is reduced by the edge growth. It was. With respect to this problem, as proposed in Patent Documents 4 and 5, etc., an organic EL element capable of suppressing the occurrence of edge growth has been developed. You have reached a level that does not cause problems.
JP-A-10-185684 JP 2002-296709 A JP 2001-356422 A Japanese Patent Laid-Open No. 2005-5227 JP 2001-57286 A

  However, the occurrence of edge growth over time of the organic EL element has not been completely eliminated, and the influence of edge growth when used in an exposure head has been clarified by research by the present inventors.

  When edge growth occurs and the light emitting area of the light emitting element is reduced, it is easily conceived that the exposure amount decreases. However, it is considered that this decrease in the exposure amount can be compensated by correcting the light amount deviation. However, the present inventor has found that the influence of the reduction in the light emitting area of the organic EL element is not only the reduction in the exposure amount, but the print gradation characteristics are softened in the exposure to the silver halide photosensitive material as the light emitting area is reduced. I found a phenomenon.

  FIG. 14 is a graph showing print gradation characteristics when the silver halide photosensitive material is exposed while changing the light emitting area ratio of the light emitting element between 100% and 55%. Here, the light emission area ratio is the ratio of the light emission area to the initial light emission area when the initial light emission area is 1. Here, the exposure amount change accompanying the change in the light emission area ratio is corrected. From FIG. X, it is apparent that the print gradation characteristics become soft as the light emitting area ratio of the light emitting element decreases. That is, exposure to silver halide light-sensitive materials using an organic EL element array may cause an important print quality problem even if the light emission area change is small enough not to be noticed by the display. In addition, the correction method as described in Patent Document 1 in which the light amount is corrected by measuring the light amount under one predetermined exposure condition (drive current, lighting time) cannot obtain an image with a desired print density. Became clear.

  On the other hand, if the gradation correction by the method described in Patent Document 3 is periodically performed, it is considered possible to correct the temporal gradation change due to the edge growth as a result. In order to correct the gradation characteristics with high accuracy, photometry of about 16 to 20 gradations is required, and the photometry time becomes very long, which is a problem in practical use.

  In addition to organic EL elements, LEDs, PLZT, liquid crystal, VFTH, and the like are employed as exposure light sources (light emitting elements) for recording images on photosensitive materials. In light emitting elements other than organic EL elements, No change in the emission area over time has been confirmed, and edge growth is a characteristic limited to organic EL elements.

  In view of the above circumstances, an object of the present invention is to provide an exposure apparatus that can suppress the influence of gradation change due to edge growth of an organic EL element and can obtain a stable print quality.

The first exposure apparatus of the present invention includes an optical scanning exposure head in which a large number of light emitting elements made of organic EL elements are arranged in the main scanning direction, and the optical scanning exposure is performed in the sub-scanning direction intersecting with the main scanning direction. In an exposure apparatus that forms an image based on image data on a photosensitive medium that moves relative to a head,
Gradation characteristic data storage means for storing gradation characteristic data in the photosensitive medium when the light emitting element emits light in each light emitting area in association with each light emitting area that the light emitting element changes;
A light emitting area obtaining means for obtaining a light emitting area of the light emitting element that has changed over time;
Gradation characteristic selection means for selecting gradation characteristic data corresponding to the light emission area obtained in the light emission area acquisition means from the gradation characteristic data storage means;
And a gradation converting means for performing gradation conversion based on the selected gradation characteristic data.

The second exposure apparatus of the present invention comprises an optical scanning exposure head in which a large number of light emitting elements made of organic EL elements are arranged along the main scanning direction, and the optical scanning exposure in the sub-scanning direction intersecting with the main scanning direction. In an exposure apparatus that forms an image based on image data on a photosensitive medium that moves relative to a head,
Gradation characteristic data storage means for storing basic gradation characteristic data in the photosensitive medium when the light emitting element emits light with a predetermined light emitting area, and gradation correction coefficient for each light emitting area that changes in the light emitting element;
A light emitting area obtaining means for obtaining a light emitting area of the light emitting element that has changed over time;
A gradation characteristic selection means for selecting a gradation correction coefficient corresponding to the light emission area obtained in the light emission area acquisition means from the gradation characteristic data storage means;
Gradation conversion means for correcting the basic gradation characteristic data based on the selected gradation correction coefficient and performing gradation conversion based on the corrected basic gradation characteristic data; Is.

  The light emitting area of the light emitting element changes with time. Here, “every light emitting area changed with the light emitting element” means every light emitting area changed with time.

  The light emitting area that has changed with time of the light emitting element, which is obtained by the light emitting area acquisition means, does not necessarily have to be an absolute value, and even if the rate of change of the light emitting area with time (light emitting area ratio = light emitting area / initial light emitting area) Good.

  In each of the above-described exposure apparatuses, the light emission area acquisition unit includes a photometric unit that measures a beam profile of emitted light from a predetermined one or a plurality of light emitting elements among a plurality of light emitting elements, and a light emitting element based on the beam profile. And a calculation means for obtaining the light emitting area.

  The photometric unit may acquire a two-dimensional beam profile, or may acquire a one-dimensional beam profile such as a main scanning direction or a sub-scanning direction.

  In particular, the photometric means measures the beam profile in the main scanning direction as the beam profile in a state where the predetermined one or a plurality of light emitting elements are lit in isolation, and the computing means is the main scanning direction. It is preferable that the light emission area is obtained based on the beam spread amount in the main scanning direction obtained from the beam profile.

  Alternatively, the photometric means measures the beam profile in the main scanning direction as the beam profile in a state where a plurality of light emitting elements adjacent to each other including the predetermined one or a plurality of light emitting elements are lit. Light emission in the vicinity of the middle of the light emission element adjacent to the central light emission intensity in the main scanning direction of the predetermined one or more light emitting elements, which is obtained from the beam profile in the main scanning direction. It is desirable to obtain the light emitting area based on the ratio to the intensity.

The first gradation correction method of the present invention comprises an optical scanning exposure head in which a large number of light emitting elements made of organic EL elements are arranged along the main scanning direction, and the light is emitted in the sub-scanning direction intersecting with the main scanning direction. A gradation correction method in an exposure apparatus that forms an image based on image data on a photosensitive medium that moves relative to a scanning exposure head,
In association with each light emitting area where the light emitting element changes, gradation characteristic data in the photosensitive medium when the light emitting element emits light in each light emitting area is stored in advance.
Obtaining the light emitting area changed over time of the light emitting element,
Selecting gradation characteristic data corresponding to the determined light emitting area from the previously stored gradation characteristic data;
The gradation conversion is performed based on the selected gradation characteristic data.

The second gradation correction method of the present invention comprises an optical scanning exposure head in which a large number of light emitting elements composed of organic EL elements are arranged along the main scanning direction, and the light is emitted in the sub-scanning direction intersecting the main scanning direction. A gradation correction method in an exposure apparatus that forms an image based on image data on a photosensitive medium that moves relative to a scanning exposure head,
Basic gradation characteristic data in the photosensitive medium when the light emitting element emits light with a predetermined light emitting area, and a gradation correction coefficient for each light emitting area that changes in the light emitting element are stored in advance.
Obtaining the light emitting area changed over time of the light emitting element,
A gradation correction coefficient corresponding to the obtained light emitting area is selected from the previously stored gradation correction coefficients;
The basic gradation correction data is corrected using the selected gradation correction coefficient, and gradation conversion is performed based on the corrected gradation characteristic data.

  When obtaining the light emitting area that has changed over time of the light emitting element, it is not always necessary to obtain the absolute value thereof, and the rate of change over time of the light emitting area (light emitting area ratio = light emitting area / initial light emitting area) may be obtained.

  In each of the gradation correction methods, a beam profile of light emitted from a predetermined one or a plurality of light emitting elements among the plurality of light emitting elements is measured, and a light emitting area of the light emitting element is obtained based on the beam profile. can do.

  The beam profile may be a two-dimensional beam profile or a one-dimensional beam profile such as a main scanning direction or a sub-scanning direction.

  In particular, as the beam profile, the beam profile in the main scanning direction is measured in a state where the predetermined one or a plurality of light emitting elements are lit in isolation, and the light emission area is obtained from the beam profile in the main scanning direction. It is desirable to obtain it based on the amount of beam spread in the main scanning direction.

  Alternatively, as the beam profile, in a state where a plurality of light emitting elements adjacent to each other including the predetermined one or a plurality of light emitting elements are turned on, the beam profile in the main scanning direction is measured, Based on the ratio of the center emission intensity in the main scanning direction of the one or more light emitting elements obtained from the beam profile in the main scanning direction and the emission intensity in the vicinity of the intermediate between the light emitting elements and the adjacent light emitting elements. It is desirable that

  The first exposure apparatus of the present invention includes a gradation characteristic data storage unit that stores gradation characteristic data for each light emitting area that changes in the light emitting element, a light emitting area acquisition unit that obtains a light emitting area of the light emitting element, and a light emitting area. Since the gradation characteristic selecting means for selecting the corresponding gradation characteristic data and the gradation converting means for performing gradation conversion based on the selected gradation characteristic data are provided, the organic EL light emitting element is changed over time. Therefore, it is possible to correct gradation fluctuations accompanying a decrease in the light emitting area, and to provide a long-term stable print quality.

  The second exposure apparatus of the present invention comprises a gradation characteristic data storage means for storing basic gradation characteristic data and a gradation correction coefficient for each light emission area, a light emission area acquisition means for obtaining a light emission area of the light emitting element, Tone characteristic selecting means for selecting a gradation correction coefficient corresponding to the light emitting area, and correcting the basic gradation characteristic data based on the selected gradation correction coefficient, and based on the corrected basic gradation characteristic data Since gradation conversion means for gradation conversion is provided, it is possible to correct gradation fluctuations accompanying a decrease in the light emitting area with time of the organic EL light emitting element, and to provide stable print quality over the long term. be able to. Further, since only the gradation correction coefficient is stored for each light emitting area, the memory of the storage means can be kept small as compared with the first exposure apparatus.

  Note that the light emitting area acquisition means includes a photometric means for measuring a beam profile of light emitted from a predetermined light emitting element or a plurality of light emitting elements, and an operation for obtaining a light emitting area of the light emitting element based on the beam profile. If a device that measures the beam profile in the main scanning direction is used as the photometric means, it can also be used as a photometric means at the time correction of a general light amount deviation, and it is based on edge growth. There is no need for a dedicated light receiver or detection operation only for gradation correction, and an increase in cost and correction time can be suppressed.

  According to the first gradation correction method of the present invention, gradation characteristic data for each light emitting area of the light emitting element is stored in advance, the light emitting area that has changed with time is obtained, and the light emitting area corresponding to the obtained light emitting area is obtained. Since gradation conversion is performed by selecting gradation characteristic data, it is possible to correct gradation fluctuations associated with a decrease in the light emitting area over time of the organic EL light emitting element, and to provide long-term stable print quality. Can do.

  In the second gradation correction method of the present invention, basic gradation characteristic data of a light emitting element and a gradation correction coefficient for each light emitting area are stored in advance, and a light emitting area that has changed with time is determined. A gradation correction coefficient corresponding to the obtained light emitting area is selected, the basic gradation correction data is corrected using the selected gradation correction coefficient, and gradation conversion is performed based on the corrected gradation characteristic data. As a result, gradation fluctuations associated with a decrease in the light emitting area over time of the organic EL light emitting element can be corrected, and stable print quality can be provided over the long term.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a partially broken front view of a printing system 5 which is an embodiment of the exposure apparatus of the present invention, FIG. 2 is a partially broken side view of the printing system 5, and FIG. 3 is used for an exposure head 1 of the printing system 5. FIG. 4 is a block diagram showing a schematic configuration of the printing system 5, and FIG. 5 is a block diagram showing details of the drive circuit 30.

  The printing system 5 conveys the exposure head 1 and the color photosensitive material 3 held at the position where the exposure light 2 emitted from the exposure head 1 is irradiated at a constant speed in the direction of arrow Y in FIG. A sub-scanning means 4, a drive circuit 30 that drives the exposure head 1, a light emission control unit 40 that outputs a signal such as a light emission timing to the drive circuit 30, a system control unit 45 that controls the entire apparatus, And a photometric inspection device 50 for light amount deviation correction and gradation correction.

  The exposure head 1 is arranged at a position where the organic EL panel 6 and the exposure light 2 emitted from the organic EL panel 6 are received, and an image formed by the exposure light 2 is formed on the color photosensitive material 3 at the same magnification. And a holding means 8 (not shown in FIG. 2) for holding the lens array 7 and the organic EL panel 6.

  As shown in detail in FIG. 3 which is a plan view thereof, the gradient index lens array 7 which is an equal-magnification imaging lens array includes a minute gradient index lens 7a for condensing the exposure light 2 in the sub-scanning direction. A total of two lens rows arranged in parallel in the main scanning direction (arrow X direction) perpendicular to Y are arranged. In the gradient index lens array 7, the gradient index lenses 7a are arranged in a staggered manner. That is, the plurality of gradient index lenses 7a constituting one lens row are arranged so as to be positioned between the plurality of gradient index lenses 7a constituting the other lens row.

  The printing system 5 of the present embodiment exposes a color image onto a color photosensitive material 3 which is a full color positive type silver salt photographic photosensitive material (silver halide photosensitive material) as an example, and an organic EL panel constituting the exposure head 1. 6 includes a red line-shaped light emitting element array 6R, a green line-shaped light emitting element array 6G, and a blue line-shaped light emitting element array 6B that are arranged side by side in the sub-scanning direction Y. Each of the line-shaped light emitting element arrays 6R, 6G, and 6B includes a large number of red organic EL light emitting elements, green organic EL light emitting elements, and blue organic EL light emitting elements arranged in parallel in the main scanning direction X.

  In FIG. 1 and FIG. 2, one of the light emitting elements is typically shown as an organic EL light emitting element 20. Each organic EL light emitting element 20 is formed by sequentially laminating a transparent anode 21, an organic compound layer 22 including a light emitting layer, and a metal cathode 23 on a transparent substrate 10 made of glass or the like. Then, red light emitting elements, green light emitting elements, and blue light emitting elements are respectively applied as the light emitting layers, thereby forming red organic EL light emitting elements, green organic EL light emitting elements, and blue organic EL light emitting elements, respectively.

  Elements constituting each organic EL light emitting element 20 are arranged in a sealing member 25 made of, for example, a stainless steel can. That is, the edge of the sealing member 25 and the transparent substrate 10 are bonded, and the organic EL light emitting element 20 is sealed in the sealing member 25 filled with dry nitrogen gas.

  In the organic EL light-emitting device 20 having the above-described configuration, when a voltage is applied between the metal cathode 23 and the transparent anode 21 extending across the metal cathode 23, an organic compound layer is formed at each intersection of the electrodes to which the voltage is applied. A current flows through 22 and the light emitting layer contained therein emits light. The emitted light passes through the transparent anode 21 and the transparent substrate 10 and is emitted as exposure light 2 to the outside of the device.

  The system control unit 45 shown in FIG. 5 is composed of a one-chip CPU, and although not shown, controls the entire printer through various operation switches or communication with the outside, receives image data from the outside, and performs image processing operations. Thereafter, necessary image data, various correction data, and the like are sent to the light emission control unit to perform the exposure operation. Further, the system control unit 45 has a function as a calculation means 47 and a gradation characteristic selection means 48 which are a part of a light emission area acquisition means described later for carrying out the gradation correction method of the present invention.

  The light emission control unit 40 includes a light emission timing control circuit 41, a gradation conversion unit 42, a light amount deviation correction circuit 43, a light amount correction coefficient memory 44, and a gradation characteristic data storage unit 46. From the system control unit 45, The image data to be sent is converted into a target exposure amount that matches the characteristics of the photosensitive material in the gradation conversion means 42, and the light amount deviation correction calculation is performed in the light amount correction circuit 43 to obtain the light emission time for each light emitting element. Output to 30. The light amount deviation correction calculation is an operation for obtaining the light emission time for each light emitting element by multiplying the light amount correction coefficient for each light emitting element stored in the light amount correction coefficient memory 44 by the target exposure amount. The driving circuit 30 performs driving corresponding to the input light emission time. Note that the gradation characteristic data and the light amount correction coefficient are set by the system control unit 45 prior to printing.

  The line-shaped light emitting element arrays 6R, 6G, and 6B are driven by the drive circuit 30. The drive circuit 30 sets the cathode cathode 31 that sequentially sets the metal cathode 23 that becomes the scanning electrode to the ON state at a predetermined cycle, and sets the transparent anode 21 that becomes the signal electrode to the ON state based on the image data D indicating a full-color image. The line-shaped light emitting element arrays 6R, 6G, and 6B are driven by a so-called passive matrix line sequential selection driving method. The operation of the drive circuit 30 is controlled by the above-described light emission control unit 40 that corrects the image data D and outputs it as data D ′.

  FIG. 5 is a block diagram of the drive circuit 30 for driving the organic EL array. As an example, a constant current drive for the passive matrix of the anode 480ch and the cathode 3ch and a PWM modulation type organic EL driver are shown. In FIG. 5, the cathode driver 31 and the anode driver 32 are provided with 3ch and 480ch, respectively, but only one drive control unit is shown.

  The anode 480ch corresponds to the light emitting element in the main scanning direction, the cathode 3ch corresponds to the RGB three-color light emitting element array, and in the drive circuit 30, the anode is driven with a constant current with one cathode selected, and each element is controlled by PWM. Controls the light emission time.

  The shift register 33 receives the serial load clock SR CLK and the 8-bit data signal Data, and also receives the serial load signal SR Load. At this time, while driving one cathode (for example, R2), the light emission time data for 480 elements for the next cathode (for example, R3) is transferred to the shift register 33 as an 8-bit data signal Data synchronized with the SR CLK signal. accumulate.

  The light emission time data stored in the shift register 33 is transferred to the 8-bit PWM circuit 34 every time the SR Load signal is input.

  In the 8-bit PWM circuit 34, the light emission time data for the above 480 elements is converted into a 256-step light emission pulse voltage signal PWMout by the PWM CLK signal and input to the anode driver 32. In response to this signal, each light emitting element is driven by a constant current pulse by the anode driver 32.

  The anode driver 32 has a drive control unit that is individually connected to each of the 480 transparent electrodes 21. The drive control unit includes a constant current source and a switching unit that connects the constant current source and the transparent anode.

  PWM CLK is input to the timing generation circuit 36 of the drive circuit 30, and the operations of the current voltage setting unit 35 and the line counter / decoder unit 37 are controlled based on this signal.

  As shown in FIG. 5, the cathode driver 31 has switching portions R1, R2 and R3 interposed in lines individually connected to the three metal cathodes 23. The cathode driver 31 is connected to a line counter / decoder 37 for receiving a signal from the timing generation circuit 36 as shown in FIG. The cathode driver 31 controls the metal cathodes 23 to be sequentially driven based on signals from the line counter / decoder unit 37.

  The setting of the drive current and the drive voltage by the cathode driver 31 and the anode driver 32 is basically controlled based on the output from the current / voltage setting unit 35.

  Here, the number of pixels in the main scanning direction of the line-shaped light emitting element arrays 6R, 6G, and 6B, that is, the number of arranged transparent anodes 21 is 460. When the color photosensitive material 3 is subjected to image exposure, the color photosensitive material 3 is conveyed by the sub-scanning means 4 at a constant speed in the arrow Y direction. In synchronism with the conveyance of the color photosensitive material 3, one of the three metal cathodes 23 is sequentially selected to be in the ON state by the cathode driver 31 of the drive circuit 30 described above.

  In this way, the anode driver 32 of the drive circuit 30 is connected to the first, second, third,... Within the period when the first metal cathode 23, that is, the metal cathode 23 constituting the red line-shaped light emitting element array 6R is selected. .. 460 Each transparent anode 21 of 460 corresponds to image data D indicating the red density of the first, second, third,..., 460th pixels of the first main scanning line (the time can be corrected). However, this will be described later) and connected to a constant current source. As a result, a current having a pulse width corresponding to the image data flows through the organic compound layer 22 between the transparent anode 21 and the metal cathode 23, and red light is emitted from the organic compound layer 22.

  Thus, the exposure light 2 which is red light emitted from the red line-shaped light emitting element array 6R is condensed on the color photosensitive material 3 by the lens array 7, and thereby the first main scanning line is formed on the color photosensitive material 3. The first, second, third,..., 460th pixels constituting the pixel are exposed to red light, and develop a red color.

  Next, within a period in which the second metal cathode 23, that is, the metal cathode 23 constituting the green line-shaped light emitting element array 6G is selected, the anode driver 32 of the drive circuit 30 has the first, second, third,. Each of the transparent anodes 460 is connected to a constant current source for a time corresponding to image data indicating the green density of the first, second, third,... 460th pixels of the first main scanning line. As a result, a current having a pulse width corresponding to the image data flows through the organic compound layer 22 between the transparent anode 21 and the metal cathode 23, and green light is emitted from the organic compound layer 22.

  Thus, the exposure light 2 which is green light emitted from the green line-shaped light emitting element array 6G is condensed on the color photosensitive material 3 by the lens array 7, and thereby the first main scanning line is formed on the color photosensitive material 3. The first, second, third,..., 460th pixels constituting the pixel are exposed to green light and are colored green. Since the color photosensitive material 3 is conveyed at a constant speed as described above, the green light is irradiated onto a portion of the color photosensitive material 3 that has already been exposed to red light.

  Next, within the period when the third metal cathode 23, that is, the metal cathode 23 constituting the blue line-shaped light emitting element array 6B is selected, the anode driver 32 of the drive circuit 30 has the first, second,. Each of the transparent anodes 460 is connected to a constant current source for a time corresponding to the image data indicating the blue density of the first, second, third,... 460th pixels of the first main scanning line. As a result, a current having a pulse width corresponding to the image data flows through the organic compound layer 22 between the transparent anode 21 and the metal cathode 23, and blue light is emitted from the organic compound layer 22.

  Thus, the exposure light 2 which is blue light emitted from the blue line-shaped light emitting element array 6B is condensed on the color photosensitive material 3 by the lens array 7, and thereby the first main scanning line is formed on the color photosensitive material 3. The first, second, third,..., 460th pixels constituting the pixel are exposed with blue light, and develop a blue color. Since the color photosensitive material 3 is conveyed at a constant speed as described above, the blue light is irradiated onto the portion of the color photosensitive material 3 that has already been exposed to red light and green light. Through the above steps, the first full-color main scanning line is exposed and recorded on the color photosensitive material 3.

  In the following, the same operation is repeated to expose the second full-color main scanning line. Further, such color main scanning lines are successively exposed in the sub-scanning direction Y, and a large number of color main scanning lines 3 are exposed on the color photosensitive material 3. A two-dimensional color image consisting of main scanning lines is exposed. In the present embodiment, as described above, each color exposure light is subjected to pulse width modulation, and the amount of emitted light is controlled corresponding to the image data, whereby a color gradation image is exposed.

  Next, a light quantity deviation correction method for preventing the above-described streak unevenness from occurring in the exposure image due to variations in light emission characteristics of the organic EL light emitting element 20 and light quantity deviation due to the lens array 7 is as follows.

  The means for performing the light amount deviation correction includes a system control unit 45, a light emission control unit 40, and a photometric inspection device 50. First, the configuration and photometric processing of the photometric inspection device 50 will be described. A schematic configuration of the photometric inspection apparatus 50 is shown as a block diagram in FIG. FIGS. 6 and 7 show the front shape and planar shape of the photometric means 55 of the photometric inspection device 50, respectively. As shown in FIG. 4, the photometric inspection device 50 includes a photometric means 55, a photometric timing control circuit 56 for controlling the photometric timing by the photometric means 55, an amplifier 57 for amplifying a signal from the photometric means 55, an analog signal, Is converted to a digital signal, and a CPU 59 is provided for calculating light quantity correction data. As shown in FIGS. 6 and 7, the photometric means 55 includes a light receiver 51 disposed at the same position as the position where the color photosensitive material 3 is disposed at the time of image exposure, and holds and guides the light receiver 51. The moving means 53 loaded on 52 and the light shielding member 54 that covers the light receiving surface in a state where only a part of the light receiving surface of the light receiver 51 is viewed.

  The moving means 53 is formed to be intermittently movable along the guide 52 in the direction in which the lenses 7a of the lens array 7 are arranged. Further, in this example, the alignment pitch (hereinafter referred to as element pitch) of the organic EL light emitting elements 20 of the line light emitting element arrays 6R, 6G and 6B is 100 μm, and the moving means 53 is intermittently moved. The pitch (photometric pitch) is 5 μm. Further, the light shielding member 54 has an elongated slit 54a extending in a direction perpendicular to the moving direction of the moving means 53, and the light receiving surface of the light receiver 51 is exposed only at the slit 54 portion. The width of the slit 54a, that is, the photometric aperture length is 5 μm, which is the same as the photometric pitch.

  In the photometry process, first, the moving means 53 sends image data corresponding to the pulse width for performing the light amount correction operation from the system control unit 45 of the printing system 5 arranged on one end side of the guide 52. At this time, the light quantity correction coefficients are all set to 1, and all elements on one line arranged in the main scanning direction are caused to emit light with the same light emission pulse width. For example, all of the organic EL light emitting elements 20 in the red line light emitting element array 6R are supplied with a constant current based on a common light emission command signal, so that they are lit or isolated (all elements on one line) Are lit at the same time. Next, whenever the moving means 53 moves intermittently as described above and stops, the amount of light emitted from the lens array 7 is measured by the light receiver 51. Photometry is performed for each line, and the light amount of each element is measured in the same procedure for the green line light emitting element array 6G and the blue line light emitting element array 6B.

  In the CPU 59 of the photometric inspection device 50 shown in FIG. 4, the light quantity measurement signal input from the light receiver 51 of the photometric means 55 is divided into sections (100 μm) equal to the arrangement pitch 10 for each organic EL light emitting element 20. Integrate with respect to. Specifically, in the present embodiment, for one organic EL light-emitting element 20, the measurement light amounts for a total of 20 photometry points, 10 points on the one side in the main scanning direction and 10 points on the other side from the element center, are summed up. An average value (moving average value) multiplied by 1/20 is obtained.

  In this case, it is not necessary to accurately determine the center position of the organic EL light emitting element 20, and it is confirmed that the 20 measurement points are distributed to the left and right from the center of the organic EL light emitting element 20. I can do it. For this purpose, for example, the center of the light emitting element exists between the measurement point A where the maximum value of the light amount is measured and the measurement point B where the measurement light amount is larger among the two adjacent measurement points of the measurement point. Therefore, 10 points (including measurement point A) from the measurement point A to the opposite side of the light emitting element center and 10 points (including measurement point B) from the measurement point B to the opposite side of the light emission element center are related to a total of 20 points. What is necessary is just to use the measurement light quantity for calculation of a moving average value.

  It should be noted that the photometric accuracy can be increased by integrating a plurality of light emission pulses rather than the integration value of one light emission pulse.

  This integrated light amount is a value corresponding to the exposure amount, and the CPU 59 obtains light amount correction data for correcting the deviation of the integrated light amount and transfers it to the printing system 5.

  Instead of intermittently moving the light receiver 51 as described above for photometry, a light receiving element array 60 in which elongated light receiving elements 61 are arranged in parallel in the direction in which the organic EL light emitting elements 20 are arranged as shown in FIG. It can also be used. In that case, the width of the light receiving element 61 becomes the photometric aperture length, and the arrangement pitch of the light receiving elements 61 becomes the photometric pitch.

  In the present printing system, light quantity deviation correction is performed in the following procedure.

  First, the light quantity on the exposure surface for each element is measured by the above-described photometric inspection apparatus 50. In the system control unit 45, a light amount correction coefficient for each element 20 is obtained based on the light amount correction data transferred from the photometric inspection device 50, and the light amount correction coefficient is associated with each organic EL light emitting element 20 to control light emission. The light quantity correction coefficient memory 44 in the unit 40 is stored.

  When the light emission control unit 40 performs image exposure based on the image data D as described above, the new correction coefficient related to the organic EL light emitting element 20 is added to the image data D for causing the organic EL light emitting element 20 to emit light. Multiply to obtain correction data D ′. Therefore, the correction data D ′ is input to the drive circuit 30, and the light emission amount of each organic EL light emitting element 20 is controlled based on the correction data D ′.

  The light quantity deviation correction is performed for each of the line-shaped light emitting element arrays 6R, 6G, and 6B. Therefore, the light emission amount of each of the organic EL light emitting elements 20 of the line light emitting element arrays 6R, 6G, and 6B at the time of image exposure is compensated so as to eliminate the light amount deviation characteristic, and the unevenness in the exposed image is caused by the light quantity deviation characteristic. Occurrence is prevented.

  Next, the gradation correction method of the present invention adapted to the printing system will be described. In the printing system 5, a light emission area acquisition unit is configured by the photometric inspection device 50 and the calculation unit 47 of the system control unit 45. The light emission area acquisition unit, the gradation characteristic selection unit 48, and the gradation characteristic data storage unit. 46 and the gradation conversion means 42 constitute means for performing gradation correction. That is, the system control unit 45 obtains the light emission area from the beam profile in the calculation means 47, and the gradation characteristic selection means 48 stores the gradation characteristic data stored in the gradation characteristic data storage means 46 based on the obtained light emission area. Among them, the gradation characteristic data stored in association with the light emitting area is selected and set.

  The gradation characteristic data storage means 46 of the light emission control unit 40 associates each light emission area of the light emitting element with the gradation characteristic data in the photosensitive medium 3 when the light emitting element emits light in each light emission area. Is stored in advance. The gradation characteristic data is, for example, a print gradation conversion table that is optimal for each light emitting area. Since the gradation characteristics and the change over time of the gradation characteristics depend on the material of the photosensitive medium 3 and the material of the light emitting element, it is preferable to prepare them for each representative combination.

  The light emitting area is not an absolute value, and for example, the initial light emitting area may be 1, and the light emitting area ratio represented by the ratio of the light emitting area after aging to the initial light emitting area may be used. Specifically, for typical combinations of photosensitive materials and organic EL elements, the emission area ratio is 100%, 95%, 90%, 85%, etc. every 5%, or every 10%. The gradation characteristic is measured, and a print gradation conversion table that is optimum for each light emission area ratio is stored in the gradation characteristic data storage means 46 as gradation characteristic data.

  The beam profile data (photometric data) in the main scanning direction measured by the photometric inspection device 50 when the light amount deviation correction is performed is sent to the system control unit 45.

  The system control unit 45 obtains an average light emission area of the light emitting element array from the beam profile in the calculation means 47, and based on the light emission area, the gradation characteristic selection means 48 stores the levels stored in the gradation characteristic data storage means 46. Of the gradation characteristic data, the gradation characteristic data stored in association with the light emitting area is selected and set. The selected gradation characteristic data is sent to the gradation converting means 42. The gradation converting means 42 converts the image data of the photosensitive material based on the selected gradation characteristic data (print gradation conversion table). Conversion (gradation conversion) to a target exposure amount that matches the characteristics. As a result, gradation conversion with gradation correction can be performed.

  Further, instead of storing a print gradation conversion table for each light emission area (rate) in the gradation characteristic data storage means 46, as another embodiment, one basic gradation conversion table and a light emission area (rate) are provided. Each gradation correction coefficient is stored in the gradation characteristic data storage means 46, and the gradation characteristic selection means 48 determines the gradation correction coefficient corresponding to the light emission area obtained by the calculation means 47 of the system control unit 45. Based on the basic gradation conversion table that is selected and set from the tone characteristic data storage means 46, the gradation conversion means 42 corrects the basic gradation conversion table using the gradation correction coefficient, and is corrected according to the light emitting area. The image data may be subjected to gradation conversion. In this case as well, gradation conversion with gradation correction can be performed as in the above embodiment.

  Next, a calculation method (estimation method) of the light emission area (rate) from the beam profile in the calculation means 47 of the system control unit 45 will be described.

  First, a method for calculating the light emission area (rate) when the main scanning direction beam profile is obtained by lighting the device under measurement as photometric data by the above-mentioned photometric means will be described. Here, the area change of the organic EL element array is assumed to be equal in the main scanning direction and the sub-scanning direction.

  This beam profile in the main scanning direction is naturally influenced by the length of the light emitting area in the main scanning direction (light emitting region length).

  FIG. 9 shows respective beam profiles at the just focus position of elements that emit light at two different light emission area ratios in an organic EL element array with an element pitch of 100 μm. Here, the area ratio is the ratio of the light emission area after change with time when the initial light emission area is 1, and the solid line indicates the beam profile when the light emission area ratio is 80% and the broken line indicates the light emission area ratio 60%. ing.

  As shown in the figure, it is clear that the width of the beam profile changes as the light emission area ratio changes. That is, it can be said that the light emission area ratio can be predicted from the beam profile in the main scanning direction. For example, it is possible to estimate the light emission area ratio by using, as a parameter, the width at which the light emission intensity is 50% of the element center portion, or the so-called half width, from the main scanning direction beam profile. Note that a width W indicated by a double-headed arrow in the figure is a half-value width in a beam profile having a light emission area ratio of 60%.

  FIG. 10 shows the relationship between the light emitting area ratio of the light emitting element and the beam half width in the main scanning direction. That is, as shown in FIG. 10, the beam half-value width in the main scanning direction when light was emitted with a plurality of different light emission areas using an organic EL element array equivalent to the organic EL element array used for the exposure head was obtained. If the data is provided as an LUT, the half width of the beam is obtained from the beam profile in the main scanning direction as shown in FIG. 9 during gradation conversion, and the emission area ratio at that time is obtained (estimated) based on the LUT. And gradation correction can be performed.

  Note that what is used as a parameter for obtaining the light emission area is not limited to the half width, that is, the beam width of 50% of the light emission intensity, but also the beam width in the case of a predetermined light emission intensity higher or lower than 50%. Good.

  Next, a method of calculating a light emission area (rate) when a beam profile in the main scanning direction when a row of organic EL light emitting elements arranged in the main scanning direction is simultaneously turned on as photometric data by the above-described photometry means is obtained. explain.

  FIG. 11 and FIG. 12 show beam profiles at the just focus positions of elements that emit light at two different light emission area ratios in an organic EL element array with an element pitch of 100 μm. FIG. 11 shows the beam profile when the light emission area ratio is 80%, and FIG. 12 shows the beam profile when the light emission area ratio is 60%.

  In the main scanning direction beam profile when adjacent elements are lit simultaneously as shown in FIGS. 11 and 12, the half-value widths of individual beams are the same as in the case of the beam profile in which the light emission of adjacent elements overlaps and is lit up in isolation. It is difficult to measure accurately. However, even when the light amounts of adjacent elements overlap, it can be obtained as a substitute parameter as follows.

  The ratio of the central portion light amount of each element, that is, the maximum value in FIG. 11 (FIG. 12) to the boundary portion light amount between adjacent elements (assumed to be the right adjacent element), that is, the minimum value in FIG. Obtained as a characteristic value. This characteristic value includes an error depending on the light quantity of adjacent elements when the light quantity of each element is not uniform, but it can be used as a substitute parameter for the average value of the half width by averaging the characteristic values of multiple elements. Can do.

  FIG. 13 shows the relationship between the light emission area ratio in the main scanning direction and the above characteristic values. That is, using an organic EL element array equivalent to the organic EL element array used for the exposure head, the above characteristic values when light is emitted in a plurality of different light emitting areas are measured, and the obtained data as shown in FIG. If provided, at the time of gradation conversion, the above characteristic value is obtained from the beam profile in the main scanning direction as shown in FIG. 11 (FIG. 12), and the light emission area ratio at that time is obtained (estimated) based on the LUT. And gradation correction can be performed.

  Since the beam profile is generally affected by the optical placement error of the equal magnification imaging lens and photometry means, when estimating the light emission area from the beam profile, the half width and characteristic values obtained as the above parameters are It is preferable not to use an absolute value but to use a change amount from the initial state. For example, since the half-value width is 53 μm, the emission area ratio is not predicted to be 70%, but since the half-value width has decreased by 5 μm from the initial value, it is estimated that the emission area ratio has decreased by 10% from the initial value of 80% (FIG. 10). Thus, the influence of the error can be reduced.

  In the above-described embodiment, the temporal emission area (emission area) variation due to edge growth is obtained using the beam profile in the main scanning direction measured using a photometric inspection device used for light intensity deviation correction. Alternatively, a dedicated photometer composed of a CCD area sensor or the like may be provided, and a method of performing two-dimensional photometry of the beam profile for each light emitting element may be used. However, in that case, an expensive dedicated sensor and complicated two-dimensional photometric data processing are required, and costs and measurement data processing time increase. On the other hand, if photometric means and photometric data for light intensity deviation correction are used as in the present embodiment described above, a dedicated sensor for light emission area fluctuation measurement and a detection operation process are unnecessary, and the influence of edge growth is extremely efficient. Can be corrected.

  The progress of edge growth is closely related to the element configuration (specifically, an organic EL material, etc.). In the above-described embodiment, the edge growth of the organic EL element is described as proceeding equally in the vertical direction (main scanning direction) and the horizontal direction (sub-scanning direction). May not always be the case.

  If the progress of edge growth is different in the vertical and horizontal directions, the light emission area can be obtained simply by measuring the profile in the horizontal direction (main scanning direction) if the advance speed ratio in both directions is set as a factor dependent on the element configuration. The rate can be determined.

  However, in a special case where edge growth exists only in the vertical direction and does not occur in the horizontal direction, a sensor dedicated to edge growth such as a two-dimensional CCD and sub-scanning direction scanning photometry is required.

  Moreover, in the calculation method of the light emission area of the said embodiment, there exists a possibility that it may receive the influence of disturbances, such as a dust on a light emitting element, and a dark spot, strongly. Therefore, it is desirable to average the measurement results of a plurality of elements and obtain an average light emitting area ratio of the entire light emitting element array in order to improve accuracy. However, when the number of elements to be measured increases, the time required for the gradation correction operation increases due to an increase in the number of times of light metering and the amount of calculation, so it is desirable to determine according to the use of the exposure apparatus.

  The present invention is intended to correct the gradation characteristic variation due to the edge growth of the organic EL element, but the same effect can be obtained for a light emitting element whose light emitting area varies with time like the organic EL element. Can do.

1 is a partially broken front view of a printing system to which an embodiment of the present invention is applied. Partially broken side view of the printing system The partial top view which shows the arrangement | positioning state of the line-shaped light emitting element array in the said printing system Block diagram showing schematic configuration of printing system and photometric inspection device Block diagram of drive circuit Front view of photometric means for measuring light from exposure head Plan view of the photometric means Plan view showing another example of photometric means Beam profile in the main scanning direction of light-emitting elements when isolated A graph showing the relationship between the light emission area ratio and the half width of the beam in the main scanning direction Main scanning direction beam profile when light emitting elements aligned in the main scanning direction are all lit (light emitting area ratio of light emitting elements 80%) Main scanning direction beam profile when light emitting elements aligned in the main scanning direction are all lit (light emitting area ratio of light emitting elements 60%) Graph showing the relationship between the emission area ratio and the characteristic value obtained from the beam profile Graph showing gradation characteristics change due to light emission area ratio change

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exposure head 2 Exposure light 3 Color photosensitive material 4 Subscanning means 5 Print system 6 Organic electroluminescent panel 6R Red line light emitting element array 6G Green line light emitting element array 6B Blue line light emitting element array 7 Refractive index distribution type lens array 7a Gradient index lens
20 Organic EL light emitting device
30 Drive circuit
40 Light emission controller
42 Gradation conversion means
45 System controller
46 Gradation characteristic data storage means
47 Calculation means
48 Gradation characteristics selection means
50 Photometric inspection equipment
51 Receiver
52 Guide
53 Transportation
54 Shading member
55 Photometric means
60 Photodetector array
61 Light receiving element

Claims (10)

A light-sensitive exposure head having a light-scanning exposure head in which a large number of light-emitting elements made of organic EL elements are arranged along the main-scanning direction and moving relative to the light-scanning exposure head in the sub-scanning direction intersecting the main-scanning direction In an exposure apparatus that forms an image on a medium based on image data,
Gradation characteristic data storage means for storing gradation characteristic data in the photosensitive medium when the light emitting element emits light in each light emitting area in association with each light emitting area that the light emitting element changes;
A light emitting area obtaining means for obtaining a light emitting area of the light emitting element that has changed over time;
Gradation characteristic selection means for selecting gradation characteristic data corresponding to the light emission area obtained in the light emission area acquisition means from the gradation characteristic data storage means;
An exposure apparatus comprising gradation conversion means for performing gradation conversion based on the selected gradation characteristic data. A light-sensitive exposure head having a light-scanning exposure head in which a large number of light-emitting elements made of organic EL elements are arranged along the main-scanning direction and moving relative to the light-scanning exposure head in the sub-scanning direction intersecting the main-scanning direction. In an exposure apparatus that forms an image on a medium based on image data,
Gradation characteristic data storage means for storing basic gradation characteristic data in the photosensitive medium when the light emitting element emits light with a predetermined light emitting area, and gradation correction coefficient for each light emitting area that changes in the light emitting element;
A light emitting area obtaining means for obtaining a light emitting area of the light emitting element that has changed over time;
A gradation characteristic selection means for selecting a gradation correction coefficient corresponding to the light emission area obtained in the light emission area acquisition means from the gradation characteristic data storage means;
Gradation conversion means for correcting the basic gradation characteristic data based on the selected gradation correction coefficient and performing gradation conversion based on the corrected basic gradation characteristic data; Exposure device.   The light emission area acquisition means measures a beam profile of light emitted from a predetermined one or a plurality of light emitting elements among the plurality of light emitting elements, and obtains the light emitting area of the light emitting elements based on the beam profiles. 3. The exposure apparatus according to claim 1, further comprising a calculation unit. The photometric means measures the beam profile in the main scanning direction as the beam profile in a state where the predetermined one or more light emitting elements are lit in isolation.
4. The exposure apparatus according to claim 3, wherein the calculation means obtains the light emission area based on a beam spread amount in the main scanning direction obtained from the beam profile in the main scanning direction. The photometric means measures the beam profile in the main scanning direction as the beam profile in a state where a plurality of light emitting elements adjacent to each other including the predetermined one or a plurality of light emitting elements are lit.
The calculation means emits light in the vicinity of the center between the light emission element adjacent to the central light emission intensity in the main scanning direction of the predetermined one or more light emitting elements, which is obtained from the beam profile in the main scanning direction. 4. The exposure apparatus according to claim 3, wherein the light emission area is obtained based on a ratio to intensity. A light-sensitive exposure head having a light-scanning exposure head in which a large number of light-emitting elements made of organic EL elements are arranged along the main-scanning direction and moving relative to the light-scanning exposure head in the sub-scanning direction intersecting the main-scanning direction A gradation correction method in an exposure apparatus that forms an image on a medium based on image data,
In association with each light emitting area where the light emitting element changes, gradation characteristic data in the photosensitive medium when the light emitting element emits light in each light emitting area is stored in advance.
Obtaining the light emitting area changed over time of the light emitting element,
Selecting gradation characteristic data corresponding to the determined light emitting area from the previously stored gradation characteristic data;
A gradation correction method comprising performing gradation conversion based on the selected gradation characteristic data. A light-sensitive exposure head having a light-scanning exposure head in which a large number of light-emitting elements made of organic EL elements are arranged along the main-scanning direction and moving relative to the light-scanning exposure head in the sub-scanning direction intersecting the main-scanning direction A gradation correction method in an exposure apparatus that forms an image on a medium based on image data,
Basic gradation characteristic data in the photosensitive medium when the light emitting element emits light with a predetermined light emitting area, and a gradation correction coefficient for each light emitting area that changes in the light emitting element are stored in advance.
Obtaining the light emitting area changed over time of the light emitting element,
A gradation correction coefficient corresponding to the obtained light emitting area is selected from the previously stored gradation correction coefficients;
A gradation correction method, wherein the basic gradation correction data is corrected using the selected gradation correction coefficient, and gradation conversion is performed based on the corrected gradation characteristic data.   The light emitting area of the light emitting element is determined based on the beam profile of light emitted from a predetermined one or a plurality of light emitting elements among the plurality of light emitting elements. 6. The gradation correction method according to 6 or 7. As the beam profile, the beam profile in the main scanning direction is measured in a state where the predetermined one or more light emitting elements are lit in isolation,
9. The gradation correction method according to claim 8, wherein the light emission area is obtained based on a beam spread amount in the main scanning direction obtained from the beam profile in the main scanning direction. The beam profile in the main scanning direction is measured in a state where a plurality of light emitting elements adjacent to each other including the predetermined one or a plurality of light emitting elements are turned on as the beam profile,
The light emission area is obtained from the beam profile in the main scanning direction, and the light emission in the vicinity of the center light emission intensity of the predetermined one or more light emitting elements in the main scanning direction and the light emitting element adjacent to the light emitting element. 9. The gradation correction method according to claim 8, wherein the gradation correction method is obtained based on a ratio to intensity.

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